Metabolic inhibitors will be used to help define the sequence of molecular reactions involved in the genetic transformation of Diplococcus pneumoniae (pneumococcus) by donor DNA. Potential inhibitors will be screened to find those that reversibly block one or more steps of the recombination process as exemplified by the integration of the donor DNA into the chromosome of the recipient cell. Those inhibitors which do so will then be used sequentially to determine an order of events which may be blocked. Intermediates accumulated in the presence of various inhibitors will be extracted and characterized for the state of the donor and recipient DNA's, using a variety of physical and biological assays. Data from these experiments will be correlated with previous information on the nature of the process and on the properties of transitions from one state to the next. By characterizing further intermediates we hope to define in substantially greater detail than now available the precise nature of the reactions leading to genetic recombination and related events in this system, as a guide for understanding other such systems and to provide clearly understood tools for study of DNA reactions in general.